Pluto is an ice celestial body that is the coldest in the solar system (surface temperature minus 220 ° C). NASA's spacecraft visited Pluto for the first time in 2015, the sea (inner sea) exists under thick ice, a huge white basin covered with nitrogen glaciers exists in the equatorial region, and the atmosphere of nitrogen exists. He revealed a surprised appearance such as what to do.However, the reason for these characteristics, especially the reason why the inner sea remains warm without freezing in the frigid Pluto, was a difficult problem that has not been clarified by NASA's exploration.

　The research group performed two types of numerical calculations based on the new idea that gas hydrate, which mainly traps methane between water molecules, exists between the inner sea and the ice crust.

　As a result of the first simulation, the inner sea freezes completely hundreds of millions of years ago in the absence of methane hydrate, but in the presence of methane hydrate effectively functions as a heat insulating material inside. It turns out that the sea hardly freezes. As a result of the second simulation, it was found that it takes only about 1 million years to equalize the ice crust thickness in the absence of methane hydrate, but it takes more than 2 billion years in the presence of methane hydrate.

　So far, discussions about the inner ocean have been limited to ice satellites orbiting giant gas planets.However, this discovery shows that even many ice objects that are not Pluto-type satellites can actually have a wide range of inner seas, further expanding the possibility of extraterrestrial life.

Paper information:[Nature Geoscience] Pluto's ocean is capped and insulated by gas hydrates